Since injection-moulded plastics material parts made of ABS (acrylonitrile butadiene styrene) were successfully adhesively wet-chemically metallised for the first time at the beginning of the 1960s, there has been a wealth of method developments for also adhesively metallising further industrial plastics materials, for example polyamides (PA), polybutylene terephthalate (PBT) or polycarbonate (PC) with continued-use temperatures of up to about 150° C. and thermally still more highly loadable high-performance plastics materials, for example polyetherimide (PI), polyphenylene sulfide (PPS), polyether ether ketone (PEEK) or liquid crystal polymer (LCP), for the purpose of functional and/or decorative surface finishing.
To generalise, the pretreatment of plastics material surfaces before their metallisation can be divided into the process steps of conditioning, seeding and activation.
The method step of conditioning, in particular, is of decisive importance for an adhesive metallisation. In the specialist literature an entire series of different chemical and physical methods is described for the surface pretreatment of plastics material surfaces. In particular, the chemical methods are often matched to the nature of the plastics material surface. Essential to all these methods is the opening up of the plastics material substrate surface in order to generate the required adhesive base for the metal layer to be deposited. In the chemical methods, the formation of caverns that are open to the surface and which ensure what is known as the “push-button effect” due to the undercuts and therefore lead to an adhesive metallisation is achieved by pickling or swelling and dissolving out certain components of the plastics material.
Thus, DE 100 54 544 A1 discloses a method for the chemical metallisation of surfaces, in particular of surfaces made of acrylonitrile butadiene styrene copolymers (ABS) and their blends with other polymers, in that the surfaces thereof are pickled in highly concentrated solutions of Cr(VI) ions in sulfuric acid.
It is part of the general understanding of a person skilled in the art that the aggressive pickling attack of these solutions superficially oxidatively degrades the butadiene component from the ABS substrate matrix and dissolves out the oxidation products selectively from the surface and thus allows a porous substrate surface having caverns to develop, which ensures good adhesive strength as a result of the “push-button effect” for the subsequent precious metal seeding and chemical metallisation. In addition, the pickling of the ABS surface leads to a chemical functionalisation with OH and COOH groups. The size, position and relative arrangement of the cavities with respect to one another are therefore not freely selectable, but fixed by the specific composition of the acrylonitrile butadiene styrene (ABS) used.
For the pretreatment of the surface of moulded parts made of polyamide before the currentless metallisation, EP 0 146 724 B1 discloses the treatment in a mixture of halides of the elements of the group IA or IIA of the periodic table with sulfates, nitrates or chlorides of groups IIIA, IIIB, IVA, IVB, VIA and VIIA or of non-precious metals of group VIIIA of the periodic table in a non-etching, organic swelling agent or solvent and a metal-organic complex compound of elements of the group IB or VIIIA of the periodic table.
DE 10 2005 051632 B4 also addresses the problem of pre-treating plastics materials, and especially polyamides, before chemical metallisation, using a method in which the plastics material surfaces are treated with a solution containing a halide and/or a nitrate of Na, Mg, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ca or a pickling solution containing Zn ions, said solution containing a soluble fluoride in the form of a coordination compound of the general formula M1(HF2).
With a seeding, activation and subsequent external currentless metallisation of the surface without the above-described conditioning of the plastics material surface, although a metal layer also forms, because of the low adhesion to the substrate, this metal layer is unusable for technical or decorative purposes. In addition, chromosulfuric acid is a highly toxic, carcinogenic material that is harmful to fertility. The safe handling of all surfaces to be metallised with chromosulfuric acid is therefore linked with substantial economic and ecological costs.
It is known from the prior art that by irradiating preferably metals with very short, intensive laser radiation, as available, for example, by means of modern ultrashort pulse lasers, self-organising periodic structures can be produced on the surface. In the literature, three types of laser-induced and self-organising structures are known: “cone like structures” or “spikes” (FIG. 9), “laser induced periodic surface structures” (FIG. 10) and nanospheres, not identified in more detail, which are produced when the surface is irradiated by means of circular polarised laser radiation (FIG. 11). The microstructures mentioned are produced during the laser irradiation of metals at a high intensity and short pulse length (<100 ns) as a result of the photon-phonon interaction in a self-organising process. The precise surface topography cannot be predicted, or not with an acceptable level of effort, before the laser irradiation according to the current level of knowledge. In particular, the precise position of an elevation or a valley cannot currently be predicted, or not with reasonable effort.
Nevertheless, the microstructures have the above-described structural features. These structural features allow a person skilled in the art to sensibly make use of a description of the periodic self-organising structures by means of an—optionally mean—wavelength and amplitude.
Apart from the periodic repetition of specific surface topographies, all the microstructures mentioned share the property that the mean wavelength of the microstructures is usually smaller by a multiple than the usually used dimensions of the interaction zone between the laser radiation and metal surface, so it is clear to a person skilled in the art that the forming of the microstructures cannot be influenced by the selection of the beam diameter, but can obviously be limited to the irradiated region. The forming of the microstructures is instead determined by the present fluence.
The described self-organising laser-induced microstructures are already used in a series of applications. Thus CLPs can be used to increase the absorption of electromagnetic radiation. It is furthermore known that the corresponding negative of the self-organised laser-induced microstructures can be transferred to a plastics material surface by moulding in order, for example, to couple light from an optical fibre or to be used as a safety feature.
Thus DE 10 2010 034 085 A1 describes a method for producing embossing tools, which consist of a substrate, into the surface of which embossing structures for microstructural elements, such as holograms, nanostructures or the like are introduced. The embossing structures for the microstructural elements are introduced into the surface of the substrate by means of ultrashort laser pulses of polarised electromagnetic waves or polarised electromagnetic radiation. A method of surface structuring is thus used to produce embossing tools for microstructural elements. Thus the original structure can be transferred directly to the surface of an embossing tool and film copies can be made thereof.
US 2003/0135998 A1, on the other hand, discloses a method for producing an electric connecting element, characterised by the following method steps: a) providing a substrate of a plastically deformable polymeric material; b) mechanical forming of the substrate by an embossing tool, so substantially channel-shaped indentations are produced where conductor paths are to be produced; c) coating the substrate with an electrically conductive layer; d) galvanising the substrate until the indentations are filled; and e) removing conductor material until those points of the substrate that are not to have a conductive surface are free of a metal coating. The channel-shaped indentation describes the outer geometry of the later conductor path.